Note: Product visuals are presented for illustrative purposes only and may vary slightly in colour, finish, proportions, and final installed appearance. For the most realistic representation, please refer to our Customer Gallery featuring actual installation photos.
A Battery-Free Lock for Your HDB Letterbox
The Interlock Letterbox Lock replaces your standard mailbox lock with a battery-free, keyless 3-digit combination lock — no batteries to ever replace, and no key to lose, cut, or worry about handing out to a helper who checks your mail.
How It Works
Precision-engineered dials inside a zinc-alloy housing engage a mechanical latch, and every numbered wheel has to line up on the correct 3-digit code before that latch retracts. There's no battery and no electronics anywhere in the mechanism, so it's simply immune to the single most common failure mode of digital letterbox locks: a dead battery locking you out of your own mail.
Mechanical vs Digital: Which Should You Choose?
Most people replace their letterbox lock for the same reason — no more lost keys, no more duplicates floating around with the wrong people. A 3-digit combination lock gives you exactly that keyless convenience without ever running on a battery. Most letterbox locks on the market today go the other way and use a keypad or app, which can offer nice extras like a unique code per user, but a dead battery is the most common cause of digital lock failure in HDB and condo settings — and that's the one scenario a mechanical lock simply can't experience. If you specifically want app control or individual codes for multiple people, a digital letterbox lock may suit you better; for most households, the simpler mechanical option is genuinely enough, and one less thing to ever think about again.
Built for Urban Living
Designed specifically for HDB, BTO, resale flat and condo letterboxes, the durable zinc alloy build resists wear and Singapore's humid, coastal climate, with a low-profile design that blends into any letterbox rather than looking like an obvious retrofit.
Easy to Reset
A code-reset tool (a simple SIM-pin style tool) is included, letting you quickly and securely change your combination whenever you like — useful if you've just moved in and want to set a fresh code, or simply want to rotate your combination periodically for peace of mind.
Pricing & Installation
Priced at $80, a one-time cost with professional installation included and no ongoing expense to follow — no battery to buy, no subscription, nothing further to maintain.
Real installation photos from our customers.
| Product Type | Keyless Combination Cam Lock (battery-free letterbox lock) |
|---|---|
| Unlocking Method | 3-digit mechanical combination code (0-9 per digit) |
| Material | Zinc alloy |
| Colour | Midnight Black, Mercury Silver |
| Dial Size | 42mm x 42mm (combination dial face) |
| Mounting Hole Diameter | 19mm (cutout approx. 15.8mm x 16.3mm) |
| Cam/Lever Dimensions | Cam length: 45mm, width: 16mm; thread length: 20mm; thread diameter: 23mm |
| Overall Dimensions | Diameter: 38mm; height: 44mm (17mm below mounting surface, 23mm above) |
| Rotation | 90 degrees between Open and Close positions |
| Suitable For | HDB, BTO, resale flat, and condo letterbox/mailbox doors |
Frequently Asked Questions
Have questions? We're here to help you.
Whether you need a letterbox lock for an HDB flat or a digital lock for letterbox in a condo, our design delivers low-maintenance, high-security performance. Say goodbye to keys, batteries, and bulky hardware—upgrade today for seamless mail protection.
The lock ships with a default code of 0-0-0.
- Ensure the lock is open (default code is 0-0-0).
- Find the pin hole on the side of the front lock turntable.
- Insert a pointed tool (e.g., SIM-tray pin) into the hole and hold.
- If it does not give, turn the knob slightly and retry.
- While holding, set your new 3-digit code and release to confirm.
Yes—our dimensions match standard HDB mailbox lock cutouts.
We recommend our $80 installation package for perfect alignment and warranty coverage.
No—being battery-free and fully mechanical, it only needs occasional cleaning for optimal performance.
Being a battery-free letterbox lock, we do not need any batteries to be used. Saves your hassle and your time.